Dual-Frequency Filter for DFIG Grid Event Classification
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Solution Overview
Problem
Wind turbines connected to power grids face challenges in responding to high-voltage grid events, which can cause damage due to misinterpretation of frequency deviations and inability to distinguish between different grid conditions, leading to potential shutdowns or continued operation risks.
Innovation Solution
A dual-frequency filter system is employed to differentiate between high-voltage ride-through, weak grid, and islanding events by using a high-bandwidth and low-bandwidth filter in conjunction with a phase-locked loop, allowing for controlled responses to maintain grid connection or disconnect the DFIG as necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single frequency filter is used to detect grid events, then the system can identify frequency deviations, but it cannot distinguish between different types of grid events (islanding vs. non-islanding conditions)
Solution Approach 1:
The single frequency detection function is segmented into two separate parallel filters with different bandwidths. The first filter (higher bandwidth) detects rapid frequency changes characteristic of islanding events, while the second filter (lower bandwidth) detects gradual frequency changes typical of non-islanding grid events. This segmentation allows the system to preserve both types of frequency deviation information simultaneously.
Solution Approach 2:
The system adds a new dimension to frequency detection by introducing bandwidth as a differentiating parameter. Instead of using a single filter, two filters with different bandwidth characteristics are employed, creating a two-dimensional detection space (frequency magnitude × bandwidth response) that enables discrimination between different grid event types based on their distinct frequency deviation patterns.
2Productivity
If the wind turbine continues operating during high-voltage grid events, then power generation is maintained, but equipment damage may occur due to undetected islanding conditions
Solution Approach 1:
The dual-frequency filter system performs preliminary detection and classification of grid events before the wind turbine takes protective action. By continuously monitoring frequency deviations through both filters and comparing them against predefined thresholds, the system identifies islanding conditions in advance, allowing the turbine to disconnect before equipment damage can occur, thus prioritizing reliability over continuous productivity.
Solution Approach 2:
The system implements a feedback mechanism where the outputs of both filters are continuously compared to thresholds, and the control action (continue operation or disconnect) is adjusted based on the detected frequency deviation pattern. This closed-loop feedback ensures that the turbine responds appropriately to different grid event types, maintaining productivity when safe and protecting equipment when islanding is detected.
3Measurement precision
If a dual-frequency filter system is implemented to distinguish grid events, then accurate event identification is achieved, but the system complexity increases
Solution Approach 1:
The dual-frequency filter system uses universal low-pass filter components that can be implemented using standard control system elements. Both filters process the same frequency deviation signal from the phase-locked loop, but with different bandwidth parameters. This multi-functional approach allows a single filtering assembly to perform both rapid islanding detection and gradual non-islanding event detection without requiring separate detection systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively manages high-voltage grid events by accurately identifying conditions and enabling controlled operation or shutdown, reducing the risk of damage to wind turbine components and ensuring compliance with regulatory shutdown times.
Implementation Method 1
filtering the frequency signal via a filtering assembly so as to determine whether certain types of grid conditions are present in the power grid. The filtering assembly includes a first filter connected in parallel with a second filter
Implementation Method 2
Phase locked-loops are used to track this frequency reference. However, phase-locked loops used to determine frequency can temporarily indicate artificial deviation from nominal frequency during various grid disturbances
Data Source
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AI summary
A method for controlling a dual-fed induction generator (DFIG) connected to a power grid in response to a high-voltage grid event includes receiving, via a controller, a frequency signal of the power grid. The method also includes filtering the frequency signal via a filtering assembly so as to determine whether certain types of grid conditions are present in the power grid. The filtering assembly includes a first filter connected in parallel with a second filter. The first filter has a bandwidth that is greater than the second filter. Further, the method also includes comparing output signals of the first and second filters of the filtering assembly to one or more frequency thresholds. Moreover, the method includes controlling the DFIG based on the comparison.